In the field of the industrial automation the use of robotic manipulators, for example motorized articulated arms, is known, to which tools intended to operate on pieces to be manipulated or processed can be combined. As appropriate the tool can therefore be a clamp, pincers, or punch etc., for gripping the objects to be manipulated.
In many cases the manipulators are designed to mount interchangeable tools. In this circumstance connecting devices are generally used for operatively connecting the tools to the respective manipulator.
Generally the connecting devices at present available comprise a body intended to be permanently fixed to the manipulator, for example by means of screws. The device body comprises in its turn a plurality of seats for housing corresponding coupling portions of the tool, for example holes for housing pins or clutches of the tool. The device further comprises a mechanism for engaging the coupling portions of the tool; such a mechanism is movable between a locking position, at which the coupling portions of the tool are locked in their respective seats of the body without the possibility of disengaging, and an unlocking position, at which the coupling portions of the tool are free to be taken out of the respective seats.
In practice the connecting device is fixed to the manipulator and the tool can be removably coupled to the device body.
When expected, based on the typology of tool to be used, the operative connection that the connecting devices have to put into action further comprises the electrical, pneumatic, hydraulic connections, etc., for the supply of the tool.
Besides providing the correct and practical tool-manipulator coupling, the connecting devices have to allow a tool replacement as quick and riskless as possible for the personnel of the working station which comprises the manipulator.
For example, in the field of molding plastic components, manipulators are used for gripping, handling and repositioning the pieces and/or the molds or parts thereof. The interchangeable tools combined with manipulators mostly consist of pneumatically operated clamps.
A typical connecting device widely used in this field and others, and which defines de facto a standard with which the manufacturers comply, comprises a substantially toroidal body, fixed to the manipulator, provided with seats for housing corresponding engaging pins provided on a plate fixed to the tools. The seats are arranged circumferentially around the body axis. In radially inner position with respect to the housing seats, the body comprises a plurality of ducts for feeding compressed air used for activating each time the tools constrained to the device; usually along such ducts automatic valves for opening and closing the ducts themselves are installed. The mechanism for engaging the pins of the tool is a circular ring nut provided with through openings each one consisting in a substantially circular hole joined to an eyelet whose length is lower than the diameter of the circular hole. The ring nut is coaxial to the body and is superimposed thereto such that every through openings intercept a corresponding housing seat. The ring nut is manually rotatable by the operator between a first angular unlocking position, at which the circular holes are aligned to the accommodating seats and the pins of the tool can be inserted or taken out from the respective seats for constraining or disengaging, respectively, the tool from the device, and a second angular locking position, at which the eyelets are aligned with the accommodating seats and lock the pins of the tool at their section with reduced diameter, so as to prevent the tool from disengaging from the connecting device.
In practice when a tool needs to be replaced, the operator acts on the engaging mechanism, that is to say he rotates the ring nut to move the respective holes into alignment to the seats for accommodating the pins of the tool mounted on the device. In this way the tool can be separated from the device and, therefore, from the manipulator, in order to make room for the new tool. The automatic valves are hold opened by the tool pressing against them while remaining constrained to the connecting device. When the tool is physically separated from the device, the automatic valves are operated to close the feeding of compressed air in the respective ducts.
A relevant drawback of the described connecting devices consists in that the automatic valves act too late in closing the feeding of compressed air when the tool is separated from the device. In practice, also when the ring nut is moved by the operator to the locking position, in order to release the tool, the compressed air is still fed and it is enough to keep operative the tool itself, for example it is enough to hold opened the jaws of a pneumatic clamp. Only after the tool has been separated from the device, the residual compressed air in the tool inevitably is discharged in the atmosphere and this usually causes the tool deactivation. Referring again to the example of the pneumatic clamp, the jaws close abruptly, with evident risks for the safety of the operator handling the tool.
Some tools can also severely hurt the operators and therefore it has been long felt the need of providing connecting devices which prevent the tools from abruptly deactivating when they are removed.
The same drawback can be found also in the event the tool is activated by means of pneumatic vacuum, rather than compressed air. In this case the separation of the tool from the connecting device corresponds to the immediate pressure recovery of the tool itself and the immediate deactivation thereof.
For illustration purposes, a set of connecting devices according to the known art is commercialized by the Applicant under the name of “automatic tool-replacer for QC-Series robot” (in Italian “cambia-utensile automatico per robot QC-Series”).